Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds real modeling context beyond them: the comparison is forward-looking from today, includes the borrower continuing the old payment at the new rate, and does not attempt to reconstruct the past.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the comparison being performed and then the scenario that triggers it. Dense but every clause carries meaning; only mild compression room remains.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description carries the return-value burden and does name the three computed components (remaining interest, new-loan interest, keep-payment-scenario outcome). An agent still cannot tell the exact output shape or whether a single savings figure is returned, keeping this below a 5.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 67% and the required fields (balance, rates, payments, term) are largely self-documented by the schema. The description echoes the concepts (current payment, new rate, old payment) but adds no units, constraints, or interpretation rules beyond what the schema already provides — baseline 3.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (compare) and resource (current loan vs refinance offer) with the exact scope: 'from today forward', covering remaining interest, new-loan interest, and the keep-old-payment scenario. This specificity cleanly separates it from the generic compare_loan_offers sibling without needing to name it.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit triggering question ('the new loan has a lower payment, does it actually save money'), which is a clear use context. It stops short of naming an alternative tool or stating when not to use it, so it falls short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.